The present invention relates to the field of sigma delta modulation, and, in particular discloses methods for embedding data in a sigma delta modulated stream.
Sigma delta modulators are becoming increasingly important in the digital signal processing (DSP) field and are useful in analog-to-digital (A/D) conversion, one bit processing etc.
For a full discussion of the operation of sigma delta modulators, reference is made to one of the standard texts in the field. For example, xe2x80x9cDelta-Sigma Data Convertersxe2x80x94Theory, Design and Simulationxe2x80x9d, S. Norsworthy et. al., published 1997 by IEEE Press Marketing.
Recently, companies such as Sony Inc. of Japan have announced standard audio formats such as the Super Audio(trademark) format which stores data in a sigma delta modulated form and hence it is likely that increased utilization of sigma delta modulation will arise, particularly in the audio field.
By way of example, in FIG. 1 there is illustrated a standard form of sigma delta modulator 1 which transforms an input signal 2 to an output signal 6. The input signal 2 is first added 3 to a feedback and the output is low pass filtered 4. A quantizer 5 then maps the output of filter 4 to a +1 or xe2x88x921 value which is output as a 1 bit stream 6. The output 6 is also feedback via delay loop 7 to the input 2.
In certain embodiments, the present invention provides for the storage of data streams within sigma delta modulated streams.
In accordance with a first aspect of the present invention, there is provided a method of forming a modified sigma delta modulated data stream by computing each output sample comprising: (a) calculating an output sample by a process of sigma delta modulation; (b) altering predetermined ones of a first series values to values corresponding to a data stream located within the sigma delta modulation so as to form said modified sigma delta modulator data stream; and (c) including samples of said modified sigma delta modulated data stream in the feedback path of the sigma delta modulation.
The method can further comprise (d) modifying the magnitude of other predetermined members of said first series in a manner as determined by the values of corresponding data stream values.
In accordance with a further aspect of the present invention, there is provided a sigma delta modulator, comprising: input means for inputting an input signal stream; summing means connected to said input means for adding a feedback signal stream to said input signal to produce an altered input signal stream; low pass filtering means connected to said summing means for low pass filtering said altered input signal stream to produce a low pass filtered signal stream; a quantizer for quantizing said low pass filtered signal to produce a first output signal stream; and bit stuffing means for inserting predetermined values in predetermined positions in said first output signal stream to form a final output signal stream, said final output signal stream also being fed back to said summing means so as to form said feedback signal stream.
In accordance with a further aspect of the present invention, there is provided a sigma delta modulator, comprising: input means for inputting an input signal stream; summing means connected to said input means for adding a feedback signal stream to said input signal to produce an altered input signal stream; low pass filtering means connected to said summing means for low pass filtering said altered input signal stream to produce a low pass filtered signal stream; bit stuffing means for adding predetermined values in predetermined positions in said low pass filtered signal stream to form a bit stuffed low pass filtered stream; and a quantizer for quantizing said bit stuffed low pass filtered stream to produce an output signal stream, said output signal stream also being fed back to said summing means so as to form said feedback signal stream. The predetermined values can comprise a convolution of a zero padded data input stream with at least one negative number and a unity value.
In accordance with a further aspect of the present invention, there is provided a sigma delta modulator, comprising: a summer receiving an input signal stream and a feedback signal stream, and producing an altered input signal stream; a low pass filter connected to the summer, and producing a low pass filtered signal stream; a quantizer connected to the low pass filter and producing a first output signal stream; and a bit stuffer configured to insert predetermined values in predetermined positions in said first output signal stream, and producing a final output stream, said final output stream also being fed back to the summer as the feedback signal stream.